The present invention relates to a zoom optical system for photographic cameras, and more specifically a zoom optical system for lens shutter cameras in particular.
Lens shutter cameras have generally used zoom lens systems in recent years and demands are increasing in particular for lens systems which have vari-focal ratios of 3 and higher. On the other hand, demands are increasing for compact and inexpensive lens systems.
Out of various types zoom lens systems for lens shutter cameras which are known as those having-vari-focal ratios of 3 and higher in particular, there are known many zoom lens systems each composed of three lens units having a positive-positive-negative refractive power distribution. The zoom lens system which is composed of the three lens units consists in order from the object side, for example, of a first lens unit having positive refractive power, a second lens unit having positive refractive power and a third lens unit having negative refractive power, and is configured for zooming from a wide position to a tele position by moving the lens units so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit.
An conventional examples of such a zoom lens system as that described above, there are known zoom lens system which are disclosed by Japanese Patents Kokai Publication No. Hei 11-183801, No. Hei 11-119098, No. Hei 11-52232, No. Hei 9-179025, No. Hei-9-120028, No. Hei 9-90225 and No. Hei 8-262325. These conventional examples have large total lengths at tele positions, thereby requiring complicated and large lens barrels.
Furthermore, a zoom lens system disclosed by Japanese Patent Kokai Publication No. Hei 9-33813 has a high telephoto ratio, thereby hardly allowing cameras to be configured compact.
Furthermore, a zoom lens system disclosed by Japanese Patent Kokai Publication No. Hei 8-152559 requires high precisions for airspaces and the like, thereby being hardly manufactured.
An object of the present invention is to provide a zoom lens system comprising, in order from the object side, a first lens unit having positive refractive power, a second lens unit having positive refractive power and a third lens unit having negative refractive power, and configured to change a magnification from a wide position to a tele position by moving the lens units on the object side so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, and satisfy the following conditions (1), (2), (3) and (4):
fT/fW greater than 3.8xe2x80x83xe2x80x83(1)
0 less than [S(fTa)xc2x7S(fW)]/(fTaxe2x88x92fW) less than 0.2xe2x80x83xe2x80x83(2)
0.8 less than L(fTa)/(fTaxe2x88x92fW) less than 0.2xe2x80x83xe2x80x83(3)
0 less than H(G1)/fTa less than 0.023xe2x80x83xe2x80x83(4)
Another object of the present invention is to provide a zoom optical system comprising, in order from the object side, a first lens unit having positive refractive power, a second lens unit having positive refractive power and a third lens unit having negative refractive power, and configured to change a magnification from a wide position to a tele position by moving the lens units on the object side so as to widen an airspace between the first positive lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, wherein the first lens unit consists of, in order from the object side, a negative meniscus lens element which has a concave surface on the object side and a positive lens element which has an object side surface having curvature higher than that of an image side surface, and wherein the third negative lens unit comprises, in order from the object side, a biconcave lens element, positive lens component which has an object side surface having curvature higher than that of an image side surface and a negative lens component which has curvature on an object side concave surface higher than that on an image side surface, and satisfies the following conditions (2A) and (3A):
0 less than [S(fT)xe2x88x92S(fW)]/(fTxe2x88x92fW) less than 0.2xe2x80x83xe2x80x83(2A)
0.8 less than L(fT)/(fTxe2x88x92fW) less than 1.05xe2x80x83xe2x80x83(3A)
Still another object of the present invention is to provide a zoom optical system comprising, in order from the object side, a first lens unit having positive refractive power, a second lens unit having positive refractive power and a third lens unit having negative refractive power, and configured to change a magnification from a wide position to a tele position by moving the lens units on the object side so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, wherein the third negative lens unit comprises, in order from the object side, a biconcave lens component, a positive lens component which has an object side surface having curvature higher than that of an image side surface and a negative lens component which has an object side concave surface having curvature higher than that of an image side surface, wherein at least an airspace between the second lens unit and the third lens unit is changed for focusing, and wherein the zoom optical system satisfies the following condition (10):
(xcex23T)2/[F(T)xc3x970.03] less than 60xe2x80x83xe2x80x83(10)
Still another object of the present invention is to provide an optical system comprising, in order from the object side, a first lens unit having positive refractive power, a second lens unit having positive refractive power and a third lens unit having negative refractive power, and configured to change a magnification from a wide position to a tele position by moving the lens unit on the object side so as to widen an airspace between the first lens unit and the second lens unit and narrow an airspace between the second lens unit and the third lens unit, change the airspace between the second lens unit and the third lens unit for focusing, and satisfies the following conditions (1), (4), (5) and (6):
fT/fW greater than 3.8xe2x80x83xe2x80x83(1)
xe2x80x830 less than H(G1)/fTa less than 0.023xe2x80x83xe2x80x83(4)
15 less than (xcex23T)2xe2x88x92(xcex23T)2xc3x97(xcex22T)2 less than 27xe2x80x83xe2x80x83(5)
0.3 less than f1/fTa less than 0.5xe2x80x83xe2x80x83(6)